This is not an economical way to get more water; ________, it is very expensive.
15. With the development of West China, many technicians are _____ needed there in recent years.
14. China has a lot of coal and oil, and it is rich in other rare minerals ______.
13. --- How long has he been in the army?--- Oh, he joined the army as far ____ as 1997.
12. He will be ____ for months and he told me he wouldn’t be ____ till next Saturday.
10. ____ ! There is a train coming.